Modern disc drives are commonly used in a multitude of computer environments, ranging from super computers to notebook computers, to store large amounts of data in a form that is readily available to a user. Typically, a disc drive has one or more magnetic discs that are rotated by a spindle motor at a constant high speed. Each disc has a data storage surface divided into a series of generally concentric data tracks that are radially spaced across a band having an inner diameter and an outer diameter. The data is stored within the data tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of read/write heads. Typically, each data track is divided into a number of data sectors where data is stored in fixed size data blocks.
The read/write head includes an interactive element such as a magnetic transducer. The interactive element senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the interactive element transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
Each of the read/write heads is mounted to a rotary actuator arm and is selectively positioned by the actuator arm over a pre-selected data track of the disc to either read data from or write data to the data track. The read/write head includes a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the disc, causes the head to fly adjacent to the disc surface with a desired gap separating the read/write head and the corresponding disc.
Typically, multiple center-open discs and spacer rings are alternately stacked on a spindle motor hub. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common axis. Collectively the discs, spacer rings and spindle motor hub define a disc pack assembly. The surfaces of the stacked discs are accessed by the read/write heads which are mounted on a complementary stack of actuator arms which form a part of an actuator assembly. The actuator assembly generally includes head wires which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a flex circuit connector mounted to a disc drive base deck.
When the disc drive is not in use, the read/write heads are parked in a position separate from the data storage surfaces of the discs. Typically, a landing zone is provided on each of the disc surfaces where the read/write heads are positioned before the rotational velocity of the spinning discs decreases below a threshold velocity which sustains the air bearing. The landing zones are generally located near the inner diameter of the discs.
The environment in which computers are used today is demanding. This is especially true for laptop computers which are often used while in transit. As a result, disc drives must function reliably under conditions of external shock and vibration. The external shock is quantified in terms of magnitude and duration, and disc drives are designed in accordance with specifications for operational and non-operational resistance to shocks.
Operational specifications address the levels of permissible shock while the drive is in operation. Low level shocks can cause the read/write heads to move off-track, resulting in data reading and writing errors. Non-operational specifications address the limits of shock due to handling and transit activities while the disc drive is non-operational. Non-operational shocks can cause damage to the read/write head and to the data discs.
There are at least four types of non-operational damage related to shock. Outer diameter portions of the data discs are damaged when the discs deflect and make contact with the actuator. Arm tip induced media damage can occur when the actuator arm deflects into the disc. Head induced media damage can occur when the heads impact the discs, either by the heads lifting off the media or by vibration propagating through the head arm after a shock.
Snubbers generally have been employed to limit the amount of deflection of disc drive components following a shock. Disc snubbers in particular are widely used to limit the amount of deflection of an outer edge of a disc in a disc pack. A common problem, however, with disc snubbers is associated with mechanical accumulation of tolerances. It is difficult to design a snubber which properly engages the discs through the range of mechanical tolerances which combine and stack among the numerous components in a disc drive. For example, the location of the discs is a function of base deck casting and machining tolerances, disc dimensions, top cover dimensions, spindle motor tolerances, and disc spacer dimensions. When all of these and other associated parts are joined, it is impossible to determine exactly where the edge of the disc will be located. This makes it difficult to properly position the disc snubber so as to effectively limit disc deflection.
The demand for ever-smaller disc spacings and ever-higher disc capacity has accelerated the long-felt need for a disc snubber that clearingly disengages the discs when the disc drive is operational, yet abuttingly engages the discs when the disc drive is non-operational, thus providing an improved fixed support of the disc edge to minimize deflection following an external shock.